This invention relates to new and useful improvements in the transmission of low temperature liquids such as liquefied natural gas (L.N.G.) and the like.
There is at present a relatively large and growing international trade in liquefied natural gas wherein the gas is carried in ocean going tankers from producing countries such as Algeria, to consuming countries such as France, Great Britain and the U.S.A.
The temperature of the liquefied natural gas in this transportation system is approximately -258.degree. F. since at this termperature, the liquefied natural gas (which consists mainly of methane) has a saturation pressure corresponding to atmospheric pressure.
Because of this, ship liquid natural gas containers and the large storage tanks required at the shipping and receiving ports, are constructed of relatively light gauge materials and in connection with the present invention, it should be noted that intermediate liquefied natural gas temperatures of say between -180.degree. to -130.degree. F., would result in correspondingly higher container pressures in the neighborhood of 190 P.S.I. to 530 P.S.I. which would, of course, necessitate heavier and more expensive pressure vessels for storage and transportation.
Present practice is to regassify the liquefied natural gas at the seaport and feed it directly to distribution mains or into vapor phase transmission pipelines for delivery to inland markets.
Several studies have been performed and published wherein liquefied natural gas was considered to be transformed to liquefied natural gas pipelines for the purpose of supplying inland markets and these studies have been based upon receiving the L.N.G. at the inlet to the transmission pipelines at the aforementioned low temperature of -258.degree. F. The results of such studies have been that low temperature L.N.G. pipelines would be marginally competitive with present vapor phase pipelines and they would also, of course, be subjected to high contraction stresses due to cool-down from initially ambient temperatures to the low operative temperatures which would exist. Because of this, contraction loops or bellow would most likely be required resulting in additional complications and expense. Furthermore, since much of the pipeline will be operated at low temperatures (-258.degree. F. approximately), relatively expensive low temperature materials such as 9% nickel steel and aluminum alloys would be required.